Is there any lore justification for being able to do previous expansion's sidequests?

[Cleretic]

I've always liked this way of thinking about it, especially as you can then (broadly) sequence things either by release patch or by the quest's level (or the level within the patch; Island Sanctuary are Lv 1 quests post Lv90 EW gwhaha)

It's a really good idea, but might not work if you're a really heavy roleplayer. If your character's story has been pretty thoroughly detailed across like three years in a fairly solid community and you don't necessarily have full control over it, it's gonna be hard to sell 'I've had this part of my backstory/skillset the whole time and just never mentioned it'.

But then you just pick one of the other options.